It is known that bombs with a high penetration capacity can be made to pass through concrete walls with a high modulus of rupture in compression. The thickness of such walls may be as high as 1.5 meters or even more. The modulus of rupture in compression may be of the order of 40 to 45 MPa, and values of the modulus of rupture in compression in recent concretes can be much higher than 100 MPa. Operational needs for passing through concrete walls can lead to increasingly high performance levels for penetration bombs. In particular, it may be required for them to pass through increasingly thick concrete walls with increasingly high values of the modulus of rupture in compression. Conventionally, the penetration capacity of a bomb depends on its kinetic energy. The result is that penetration difficulties increase with increased thickness of concrete and/or particularly its strength, consequently it is logical to increase the kinetic energy of the bomb, for example by varying its mass or its velocity. However, these magnitudes cannot be increased indefinitely.
A bomb is transported by a rocket to reach its objective. A rocket comprises essentially three parts. At the front it contains its guidance system and it has an engine at the back for propulsion. The warhead, in other words essentially the bomb, is located between these two elements. The dimensions, weight and velocity of rockets are fixed for versatility reasons, and for standardisation of launch ramps or standardisation of firing stations. The result is that the volume, weight and velocity of the bomb are also fixed regardless of the required performances. In particular, the kinetic energy cannot be increased so as to achieve new even higher performances. One solution could be to reinforce the structural strength of the bomb body, for example by tripling its thickness. Another solution could be to use a dense material with a significant reduction in the diameter. However, these solutions have disadvantages. The first solution makes it impossible to make a bomb body that is versatile to handle different surface or underground threats. The second solution results in a very expensive bomb body and a fairly inefficient bomb because the onboard explosive mass is then less than half the volume possible with a normal steel bomb body.
One purpose of the invention is particularly to enable a bomb with a relatively low structural mechanical strength to pass through increasingly thick or strong walls.
To achieve this, the purpose of the invention is a penetrating projectile including:                an inner tube inside which a perforating projectile is placed comprising at least one body provided with a pyrotechnic charge and a propulsion body, the body of the perforating projectile being ejected outside the tube by firing the propulsion body;        a system for controlling firing of the propulsion body, before the impact of the penetrating projectile on a target.        
For example, the perforating projectile comprises a system that determines its position inside the target as a function of time and that triggers detonation of its pyrotechnic charge at a predetermined instant. For example, this system determines the position of the perforator starting from its deceleration level characteristics in the material from which the target is made and its velocity at the point of impact on the target.
Advantageously, the inner tube includes at least two sections with different calibres, the section with the smallest calibre being oriented towards the output from the tube, the body of the perforating projectile being adapted to the output calibre of the tube, the propulsion body jamming at the transition between the two sections during ejection of the body of the perforating projectile. For example, the transition between the two sections is in the form of a cone such that the casing of the propulsion body is welded onto the cone by friction.
The body of the perforating projectile may be fixed to the casing of the propulsion body by pins.
In particular, the projectile comprises a pyrotechnic charge placed between its body and the tube containing the perforating projectile.
Another purpose of the invention is a method for penetration of a projectile according to the previous characteristics, inside a target, particularly a concrete wall. According to this method:                the perforating projectile is ejected from the tube by firing its propulsion body when the projectile is at a given distance d from the target;        since the perforating projectile penetrates into the target before the projectile, the perforating projectile detonates inside the target by firing its pyrotechnic charge to create an orifice through which the body of the projectile can pass.        
Advantageously, the perforating projectile detonates for example in the centre of the target.